A sterile, implantable component of a two-piece acetabulum prosthesis that is inserted into an acetabular shell prosthesis to provide the articulating surface with a femoral head prosthesis as part of a total hip arthroplasty (THA). It is made of polyethylene (includes hylamer, cross-linked polyethylene) and may include a stabilizing component (e.g., a ring) to limit the range of motion of the hip to help prevent dislocation.